Redox-Mediator-Assisted Electrocatalytic Hydrogen Evolution from Water by a Molybdenum Sulfide-Functionalized Metal-Organic Framework

Hyunho Noh, Chung Wei Kung, Ken Ichi Otake, Aaron W. Peters, Zhanyong Li, Yijun Liao, Xinyi Gong, Omar K. Farha, Joseph T Hupp

Research output: Contribution to journalArticle

5 Citations (Scopus)

Abstract

The Zr6-based metal-organic framework NU-1000 was successfully functionalized with candidate catalysts - MoSx units - via SIM (solvothermal deposition in MOFs) of molybdenum(VI), followed by reaction with H2S gas. The structure of the material, named MoSx-SIM, was characterized spectroscopically and through a single-crystal X-ray diffraction measurement. These measurements and others established that the catalyst is monometallic, with mixed oxygen and sulfur coordination, and that it forms from a MOF-node-supported molybdenum-based cluster featuring only oxy ligands. Notably, the formal potential for the MOF-grafted complex, like that for the metal-sulfur active site of hydrogenase, is nearly coincident with the formal potential for the hydrogen couple. Its effective concentration within the mesoporous MOF is several hundred millimolar, and its porous-framework-based immobilization/heterogenization obviates the need for aqueous solubility as a condition for use as a well-defined catalyst. MoSx-SIM was evaluated as an electrocatalyst for evolution of molecular hydrogen from aqueous acid. Although the MoSx-functionalized framework exhibits catalytic behavior, the highly insulating nature of the support inhibits high electrocatalytic performance. Introduction of an archetypal redox mediator (RM), methyl viologen (MV2+), resulted in more than 20-fold enhancement in its catalytic performance on a turnover frequency basis, implying efficient RM-assisted electron transfer to otherwise electrochemically non-addressable MoSx moieties. Electrochemical kinetic studies with additional viologens as mediators reveal an unexpected square-root dependence of overall reaction rate on mediator concentration, as well as sensitivity to the strength of RM•+ as a reductant. These observations, together with observations of potential-dependent H/D isotope effects and potential-dependent pH effects, provide useful insights into the catalysis mechanism and help to explain how the MOF-affixed monometallic catalyst can effectively catalyze a two-electron reduction reaction, i.e., hydrogen evolution from acidified water.

Original languageEnglish
Pages (from-to)9848-9858
Number of pages11
JournalACS Catalysis
Volume8
Issue number10
DOIs
Publication statusPublished - Oct 5 2018

Fingerprint

Molybdenum
Hydrogen
Metals
Catalysts
Water
Sulfur
Viologens
pH effects
Hydrogenase
Paraquat
Electrons
Electrocatalysts
Reducing Agents
Isotopes
Catalysis
Reaction rates
Solubility
Gases
Ligands
Single crystals

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)

Cite this

Redox-Mediator-Assisted Electrocatalytic Hydrogen Evolution from Water by a Molybdenum Sulfide-Functionalized Metal-Organic Framework. / Noh, Hyunho; Kung, Chung Wei; Otake, Ken Ichi; Peters, Aaron W.; Li, Zhanyong; Liao, Yijun; Gong, Xinyi; Farha, Omar K.; Hupp, Joseph T.

In: ACS Catalysis, Vol. 8, No. 10, 05.10.2018, p. 9848-9858.

Research output: Contribution to journalArticle

Noh, Hyunho ; Kung, Chung Wei ; Otake, Ken Ichi ; Peters, Aaron W. ; Li, Zhanyong ; Liao, Yijun ; Gong, Xinyi ; Farha, Omar K. ; Hupp, Joseph T. / Redox-Mediator-Assisted Electrocatalytic Hydrogen Evolution from Water by a Molybdenum Sulfide-Functionalized Metal-Organic Framework. In: ACS Catalysis. 2018 ; Vol. 8, No. 10. pp. 9848-9858.
@article{967dc2bda7a44cf5b87238f2ee18fcc2,
title = "Redox-Mediator-Assisted Electrocatalytic Hydrogen Evolution from Water by a Molybdenum Sulfide-Functionalized Metal-Organic Framework",
abstract = "The Zr6-based metal-organic framework NU-1000 was successfully functionalized with candidate catalysts - MoSx units - via SIM (solvothermal deposition in MOFs) of molybdenum(VI), followed by reaction with H2S gas. The structure of the material, named MoSx-SIM, was characterized spectroscopically and through a single-crystal X-ray diffraction measurement. These measurements and others established that the catalyst is monometallic, with mixed oxygen and sulfur coordination, and that it forms from a MOF-node-supported molybdenum-based cluster featuring only oxy ligands. Notably, the formal potential for the MOF-grafted complex, like that for the metal-sulfur active site of hydrogenase, is nearly coincident with the formal potential for the hydrogen couple. Its effective concentration within the mesoporous MOF is several hundred millimolar, and its porous-framework-based immobilization/heterogenization obviates the need for aqueous solubility as a condition for use as a well-defined catalyst. MoSx-SIM was evaluated as an electrocatalyst for evolution of molecular hydrogen from aqueous acid. Although the MoSx-functionalized framework exhibits catalytic behavior, the highly insulating nature of the support inhibits high electrocatalytic performance. Introduction of an archetypal redox mediator (RM), methyl viologen (MV2+), resulted in more than 20-fold enhancement in its catalytic performance on a turnover frequency basis, implying efficient RM-assisted electron transfer to otherwise electrochemically non-addressable MoSx moieties. Electrochemical kinetic studies with additional viologens as mediators reveal an unexpected square-root dependence of overall reaction rate on mediator concentration, as well as sensitivity to the strength of RM•+ as a reductant. These observations, together with observations of potential-dependent H/D isotope effects and potential-dependent pH effects, provide useful insights into the catalysis mechanism and help to explain how the MOF-affixed monometallic catalyst can effectively catalyze a two-electron reduction reaction, i.e., hydrogen evolution from acidified water.",
author = "Hyunho Noh and Kung, {Chung Wei} and Otake, {Ken Ichi} and Peters, {Aaron W.} and Zhanyong Li and Yijun Liao and Xinyi Gong and Farha, {Omar K.} and Hupp, {Joseph T}",
year = "2018",
month = "10",
day = "5",
doi = "10.1021/acscatal.8b02921",
language = "English",
volume = "8",
pages = "9848--9858",
journal = "ACS Catalysis",
issn = "2155-5435",
publisher = "American Chemical Society",
number = "10",

}

TY - JOUR

T1 - Redox-Mediator-Assisted Electrocatalytic Hydrogen Evolution from Water by a Molybdenum Sulfide-Functionalized Metal-Organic Framework

AU - Noh, Hyunho

AU - Kung, Chung Wei

AU - Otake, Ken Ichi

AU - Peters, Aaron W.

AU - Li, Zhanyong

AU - Liao, Yijun

AU - Gong, Xinyi

AU - Farha, Omar K.

AU - Hupp, Joseph T

PY - 2018/10/5

Y1 - 2018/10/5

N2 - The Zr6-based metal-organic framework NU-1000 was successfully functionalized with candidate catalysts - MoSx units - via SIM (solvothermal deposition in MOFs) of molybdenum(VI), followed by reaction with H2S gas. The structure of the material, named MoSx-SIM, was characterized spectroscopically and through a single-crystal X-ray diffraction measurement. These measurements and others established that the catalyst is monometallic, with mixed oxygen and sulfur coordination, and that it forms from a MOF-node-supported molybdenum-based cluster featuring only oxy ligands. Notably, the formal potential for the MOF-grafted complex, like that for the metal-sulfur active site of hydrogenase, is nearly coincident with the formal potential for the hydrogen couple. Its effective concentration within the mesoporous MOF is several hundred millimolar, and its porous-framework-based immobilization/heterogenization obviates the need for aqueous solubility as a condition for use as a well-defined catalyst. MoSx-SIM was evaluated as an electrocatalyst for evolution of molecular hydrogen from aqueous acid. Although the MoSx-functionalized framework exhibits catalytic behavior, the highly insulating nature of the support inhibits high electrocatalytic performance. Introduction of an archetypal redox mediator (RM), methyl viologen (MV2+), resulted in more than 20-fold enhancement in its catalytic performance on a turnover frequency basis, implying efficient RM-assisted electron transfer to otherwise electrochemically non-addressable MoSx moieties. Electrochemical kinetic studies with additional viologens as mediators reveal an unexpected square-root dependence of overall reaction rate on mediator concentration, as well as sensitivity to the strength of RM•+ as a reductant. These observations, together with observations of potential-dependent H/D isotope effects and potential-dependent pH effects, provide useful insights into the catalysis mechanism and help to explain how the MOF-affixed monometallic catalyst can effectively catalyze a two-electron reduction reaction, i.e., hydrogen evolution from acidified water.

AB - The Zr6-based metal-organic framework NU-1000 was successfully functionalized with candidate catalysts - MoSx units - via SIM (solvothermal deposition in MOFs) of molybdenum(VI), followed by reaction with H2S gas. The structure of the material, named MoSx-SIM, was characterized spectroscopically and through a single-crystal X-ray diffraction measurement. These measurements and others established that the catalyst is monometallic, with mixed oxygen and sulfur coordination, and that it forms from a MOF-node-supported molybdenum-based cluster featuring only oxy ligands. Notably, the formal potential for the MOF-grafted complex, like that for the metal-sulfur active site of hydrogenase, is nearly coincident with the formal potential for the hydrogen couple. Its effective concentration within the mesoporous MOF is several hundred millimolar, and its porous-framework-based immobilization/heterogenization obviates the need for aqueous solubility as a condition for use as a well-defined catalyst. MoSx-SIM was evaluated as an electrocatalyst for evolution of molecular hydrogen from aqueous acid. Although the MoSx-functionalized framework exhibits catalytic behavior, the highly insulating nature of the support inhibits high electrocatalytic performance. Introduction of an archetypal redox mediator (RM), methyl viologen (MV2+), resulted in more than 20-fold enhancement in its catalytic performance on a turnover frequency basis, implying efficient RM-assisted electron transfer to otherwise electrochemically non-addressable MoSx moieties. Electrochemical kinetic studies with additional viologens as mediators reveal an unexpected square-root dependence of overall reaction rate on mediator concentration, as well as sensitivity to the strength of RM•+ as a reductant. These observations, together with observations of potential-dependent H/D isotope effects and potential-dependent pH effects, provide useful insights into the catalysis mechanism and help to explain how the MOF-affixed monometallic catalyst can effectively catalyze a two-electron reduction reaction, i.e., hydrogen evolution from acidified water.

UR - http://www.scopus.com/inward/record.url?scp=85054326383&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85054326383&partnerID=8YFLogxK

U2 - 10.1021/acscatal.8b02921

DO - 10.1021/acscatal.8b02921

M3 - Article

AN - SCOPUS:85054326383

VL - 8

SP - 9848

EP - 9858

JO - ACS Catalysis

JF - ACS Catalysis

SN - 2155-5435

IS - 10

ER -